Abstract
Based on the ab initio (first-principles) density-functional theory calculations within the local density approximation, we investigated the ferroelectricity as well as the atomic and electronic structures at Σ5(001) twist boundaries in PbTiO_3. The twist boundary structure with the coincidence site lattice (CSL) was found to be energetically favorable. We found the coexistence of both the rectilinear polarization and the vortex in-plane polarization at the twist boundary. An applied tensile strain tends to increase the rectilinear polarization, especially at the twist boundary. The vortex polarization on the PbO layer is also enhanced with the increase of tensile strain, whereas the vortex polarization on the TiO_2 layer decreases and finally disappears at a critical strain.
